H3.7, reducedOxidation and reduction together are called redox (reduction and oxidation) and generally characterized by the transfer of electrons between chemical species, like molecules, atoms or ions, where one species undergoes oxidation, a loss of electrons, while another species undergoes reduction, a gain of electrons. This transfer of electrons between reactants Click on Term to Read More
34° 48′ N., 103° 19′ W. This 9.3 kg stone was found in Grady, New Mexico and determined to be distinct from Grady (1933), which is classified as an L chondriteOrdinary chondrites low in free Ni-Fe metal (4 to 10 vol. %), containing olivine (Fa22-26) and the orthopyroxene hypersthene (Fs19-22). Average chondrule diameters (0.7 mm) are larger than those in H chondrites. The asteroid 433 Eros is suspected as a parent body, based on reflectance spectra, but most L chondrites Click on Term to Read More. While this meteoriteWork in progress. A solid natural object reaching a planet’s surface from interplanetary space. Solid portion of a meteoroid that survives its fall to Earth, or some other body. Meteorites are classified as stony meteorites, iron meteorites, and stony-iron meteorites. These groups are further divided according to their mineralogy and Click on Term to Read More contains a total iron content (26.23 wt%) within the range of H-chondrite falls, it has Fa and Fs values well below those of normal H chondritesChondrites are the most common meteorites accounting for ~84% of falls. Chondrites are comprised mostly of Fe- and Mg-bearing silicate minerals (found in both chondrules and fine grained matrix), reduced Fe/Ni metal (found in various states like large blebs, small grains and/or even chondrule rims), and various refractory inclusions (such Click on Term to Read More (Rubin and Krot, 1993). It was likely reduced during parent bodyThe body from which a meteorite or meteoroid was derived prior to its ejection. Some parent bodies were destroyed early in the formation of our Solar System, while others like the asteroid 4-Vesta and Mars are still observable today. Click on Term to Read More metamorphism. Recent studies have provided evidence of reductionOxidation and reduction together are called redox (reduction and oxidation) and generally characterized by the transfer of electrons between chemical species, like molecules, atoms or ions, where one species undergoes oxidation, a loss of electrons, while another species undergoes reduction, a gain of electrons. This transfer of electrons between reactants Click on Term to Read More of unequilibrated ordinary chondrites corresponding to increased metamorphism, perhaps through the progressive dehydration of phyllosilicatesClass of hydroxyl-bearing silicate minerals with a sheet-like structure. They result from aqueous alteration are dominantly serpentine and smectite in meteorites; found in the matrixes of carbonaceous chondrites. Phyllosilicates consist of repeating sequences of sheets of linked tetrahedra (T) and sheets of linked octahedra (O). The T sheet consists of Click on Term to Read More. Beginning with type 4 equilibrated chondrites, the trend is reversed, and an increase in metamorphism corresponds to progressive oxidationOxidation and reduction together are called redox (reduction and oxidation) and generally characterized by the transfer of electrons between chemical species, like molecules, atoms or ions, where one species undergoes oxidation, a loss of electrons, while another species undergoes reduction, a gain of electrons. This transfer of electrons between reactants Click on Term to Read More of the chondriteChondrites are the most common meteorites accounting for ~84% of falls. Chondrites are comprised mostly of Fe- and Mg-bearing silicate minerals (found in both chondrules and fine grained matrix), reduced Fe/Ni metal (found in various states like large blebs, small grains and/or even chondrule rims), and various refractory inclusions (such Click on Term to Read More.
It was determined that the H-chondrite parent body suffered three distinct collisional events at ~7.0, 22, and 33 m.y. ago (Marti and Graf, 1992; Eugster et al.
, 2006, 2007). These ejection events produced only weak shock effects (S1–S2) and radiogenic gas loss, but injected abundant fragments into Earth-crossing resonances. The H chondrites are a good spectrographic match with the S(IV)-type asteroids 6 Hebe, 3 Juno, and 7 Iris, with 6 Hebe being the favored parent asteroid up to this time. However, hydrocode models show inconsistencies exist between expected and observed CRE ages based on the scenario of direct injection into resonances. The steady delivery of H chondriteOrdinary chondrites with a high content of free Ni-Fe metal (15-19 vol. %) and attracted easily to a magnet. Their main minerals are olivine (Fa16-20) and the orthopyroxene bronzite (Fs14.5-18.5), earning them their older name of bronzite chondrites. Chondrules average ~0.3 mm in diameter. Comparison of the reflectance spectra of Click on Term to Read More
material from 6 Hebe to Earth also remains unexplained. Studies by Rubin and Bottke (2009) led them to conclude that family-forming events resulting in large meteoroidSmall rocky or metallic object in orbit around the Sun (or another star).
reservoirs, which have homogenous compositions and locations near dynamical resonances such as the Jupiter 3:1 mean motion resonance, are the likely source of the most prevalent falls including H chondrites and HED achondrites (especially howardites). As a matter of fact, a number of asteroids having H-like mineralogies have been observed near the 3:1 (2.50 AUThe astronomical unit for length is described as the "mean" distance (average of aphelion and perihelion distances) between the Earth and the Sun. Though most references state the value for 1 AU to be approximately 150 million kilometers, the currently accepted precise value for the AU is 149,597,870.66 km. The Click on Term to Read More
) and 5:2 (2.82 AU
) resonances (Burbine et al.
, 2015 and references therein). See further details on the Abbott
Based on models comparing Pb–Pb age data with closure temperatures for chondrulesRoughly spherical aggregate of coarse crystals formed from the rapid cooling and solidification of a melt at ~1400 ° C. Large numbers of chondrules are found in all chondrites except for the CI group of carbonaceous chondrites. Chondrules are typically 0.5-2 mm in diameter and are usually composed of olivine Click on Term to Read More
and phosphates in H chondrites, it was estimated that accretionAccumulation of smaller objects into progressively larger bodies in the solar nebula leading to the eventual formation of asteroids, planetesimals and planets. The earliest accretion of the smallest particles was due to Van der Waals and electromagnetic forces. Further accretion continued by relatively low-velocity collisions of smaller bodies in the Click on Term to Read More
of the H chondrite parent body began about 1.7 m.y. after formation of CAIsSub-millimeter to centimeter-sized amorphous objects found typically in carbonaceous chondrites and ranging in color from white to greyish white and even light pink. CAIs have occasionally been found in ordinary chondrites, such as the L3.00 chondrite, NWA 8276 (Sara Russell, 2016). CAIs are also known as refractory inclusions since they Click on Term to Read More
and continued for 3.5 m.y. (Amelin et al.
, 2005). These thermal models also permitted a calculation to be made reflecting the progressive increase in petrologic types from the coreIn the context of planetary formation, the core is the central region of a large differentiated asteroid, planet or moon and made up of denser materials than the surrounding mantle and crust. For example, the cores of the Earth, the terrestrial planets and differentiated asteroids are rich in metallic iron-nickel. Click on Term to Read More
to the surface: from the core outward to a distance of 44.9 km is type 6 material; between 44.9 km and 48.9 km is type 5 material; between 48.9 km and 56.9 km is type 4 material; and from 56.9 km to the surface at 92.5 km is type 3 material.
In their modeling of the accretion and impact history of ordinary chondrites, Blackburn et al.
(2017) calculated the timing of the catastrophic disruption of the H- and L-chondrite parent bodies to be ~60 m.y. after CAIs. This timing is consistent with two competing dating techniques—U–Pb (and Hf–W) chronometry and metallographic cooling rates (Ni diffusionMovement of particles from higher chemical potential to lower chemical potential (chemical potential can in most cases of diffusion be represented by a change in concentration). Diffusion, the spontaneous spreading of matter (particles), heat, or momentum, is one type of transport phenomena. Because diffusion is thermally activated, coefficients for diffusion Click on Term to Read More
profiles in Fe-metal)—which record cooling associated with both an onion shell structure prior to disruption and a rubble pile after disruption, respectively. Utilizing Pb–phosphate age data, Edwards et al.
(2017) determined that the H and L chondrites of petrologic typeMeasure of the degree of aqueous alteration (Types 1 and 2) and thermal metamorphism (Types 3-6) experienced by a chondritic meteorite. Type 3 chondrites are further subdivided into 3.0 through 3.9 subtypes.
, those located at the greatest depths in a concentrically zoned body) show a similar timing for closure of the Pb-phosphate systemDefinable part of the universe that can be open, closed, or isolated. An open system exchanges both matter and energy with its surroundings. A closed system can only exchange energy with its surroundings; it has walls through which heat can pass. An isolated system cannot exchange energy or matter with
of ~60 m.y. after CAIs; this age reflects the occurrence of ubiquitous quenching during parent body disruption. Employing thermal models, they constrained the timing of accretion for the two parent bodies to 2.0–2.35 m.y. after CAIs, and they derived an estimate for the minimum size of the two parent bodies of ~275 km in diameter.
Another S-class asteroid, 433 Eros, recently played host to the NEAR-Shoemaker spacecraft (see NEAR’s final image below). A successful landing was followed by an unprecedented multiple spectrographic analysis of the surface. Results from this indicate that Eros has primitive Mg/Si, Al/Si, Ca/Si and Fe/Si ratios, consistent with ordinary chondriteWork in Progress Ordinary chondrites (OCs) are the largest meteorite clan, comprising approximately 87% of the global collection and 78% of all falls (Meteoritical Society database 2018)1. Meteorites & the Early Solar System: page 581 section 6.1 OC of type 5 or 6 with an apparent shock stage of S1, Click on Term to Read More
mineralogy, closely resembling H-group chondrites. Contrary to this data, the magnetometer data exclude any relationship between 433 Eros and H- or L-group chondrites, although the LL-group chondrites could not be excluded. The specimen of Grady (1937) shown above is a 3.25 g partially crusted fragment.
The surface of Eros from NEAR prior to loss of transmission.
Image measures 20 feet across. NASA photo.